1. Field of the Invention
The present invention relates to a damping force generating mechanism for generating a damping force by pressing an elastic body.
2. Description of the Background Art
A damping force generating mechanism is used for various portions required for absorbing vibration, for example, used for a so-called bottom link type suspension of a motorcycle in which a front wheel is suspended from lower end portions of a front fork through links. A general example of such a bottom link type suspension is shown in FIG. 16 (see Japanese Patent Laid-open No. Sho 62-187608).
Referring to FIG. 16, there is shown a scooter type motorcycle 01. A steering shaft 03 is turnably fitted in a head pipe 02. A pair of right and left front forked portions 04 are integrally mounted on the lower end of the steering shaft 03. A front wheel 06 is suspended from the lower ends of the front forked portions 04 through rocking arms 05 as link members.
With respect to the rocking arm 05, the base end thereof is pivotably supported on the lower end portion of the front forked portion 04, and the free end portion thereof rotatably supports the front wheel 06. A suspension spring 07 is interposed between the upper portion of the front forked portion 04 and an approximately central portion of the rocking arm 05.
A shock load applied to the front wheel from irregularities on the ground is damped by the suspension springs 07. However, when a shock load is applied with an abrupt shock load, the suspension springs are largely rebounded after being contracted once.
In an example described in Japanese Patent Publication No. Sho 57-49432, as shown in FIG. 17, a front end of a link 012 is pivotably supported on the lower end portion of a front forked portion 011 containing a hydraulic damping mechanism. A front wheel 013 is rotatably supported on a central portion of the link 012. A subcushion unit 14 is interposed between the rear end of the link 012 and the central portion of the front forked portion 011.
The subcushion unit 014 includes a cylindrical main body 015 pivotably mounted on the front forked portion 011. A piston 016 is slidably inserted in the cylindrical main body 015 and is connected to a leading end of a rod 017 pivotably mounted on the link 012. A cushion rubber 018 utilized as a damping member is inserted in the cylindrical main body 015 in such a manner as to be mounted on the upper surface of the piston 016. A stopper rubber 019 utilized as a stopper member is inserted in the cylindrical main body 015 in such a manner as to be mounted on the lower surface of the piston 016.
The subcushion unit 014 thus generates a compression side damping force by the cushion rubber 018, and also generates a tensile side damping force by the stopper rubber 019. Consequently, the subcushion unit 014 can suppress both the bound and rebound of the front wheel 013.
The above subcushion unit 014, however, has a disadvantage. Since the piston 016 is slid in the cylindrical main body 015, and the cushion rubber 018 and the stopper rubber 019 are separately provided on the upper and lower surfaces of the piston 016, the mechanism is complicated in structure, being heavy and expensive.
In view of the foregoing, an object of the present invention is to provide an inexpensive damping, force generating mechanism capable of generating both a compression side damping force and a tensile side damping force with a simple, lightweight structure.
To achieve the above object, a damping force generating mechanism is provided including an elastic body which generates a damping force when being pressed, and an internal pressure generating member inserted in the elastic body which resists the pressing force.
With this configuration, the mechanism enables a large displacement due to bending deformation of the elastic body and thereby it enables absorption of a sufficient energy. The creep generated upon bending deformation of the elastic body can be reduced by repulsion of the internal pressure generating member inserted in the elastic body accompanied by compressed deformation of the internal pressure generating member. Accordingly, a damping force generating mechanism can be obtained which is capable of reducing the characteristic change due to permanent set. The restoring ability after release of a load is also excellent due to repulsion of the internal pressure generating member.
The internal pressure generating member may comprise a spring member. With this configuration, the creep of the elastic body is reduced by repulsion of the spring member accompanied by the compression thereof. Accordingly, it is possible to make the characteristic change due to permanent set smaller and to enhance the restoring ability.
The internal pressure generating member may comprise a partitioned chamber containing a compressive gas or liquid. With this configuration, the creep of the elastic member is reduced by repulsion of a compressive gas or liquid compressed and deformed together with the partitioned chamber. Accordingly, it is possible to make the characteristic change due to permanent set smaller and to enhance the restoring ability.
The internal pressure generating member may comprise an elastic organic material. The internal pressure generating member, which is made from the organic material, can be easily molded in a shape most suitable for the application. The organic material may have a hollow portion. With this configuration, when the organic material is compressed, a specific repulsive force can be obtained by the presence of the hollow portion. The organic material may be a polyester-urethane based material. With this configuration, it is possible to obtain a specific repulsive force by a large elasticity of a polyester-urethane based material.
To further achieve the object of the invention, a damping force generating mechanism is provided which includes an elastic body which generates a damping force when being pressed, and a restricting wall for suppressing expansion of the elastic body generated in the direction perpendicular to the pressing direction of the elastic body.
When the elastic body is pressed, the expansion of the elastic body in the direction perpendicular to the pressing direction is restricted by the restricting wall. As such, the force of the elastic body applied to the restricting wall becomes larger and the sliding resistance of the elastic body is increased. As a result, a desirable relationship of load to displacement can be easily obtained by the action of the sliding resistance of the elastic body in addition to the elastic characteristic of the elastic body.
The elastic body may be separated from the restricting wall with a gap therebetween at the beginning of pressing of the elastic body, and brought into contact with the restricting wall with progressive pressing of the elastic body.
At the beginning of the pressing, since the elastic body is not brought into contact with the restricting wall due to the gap therebetween, the load is gradually increased with an increase in displacement only by the elastic characteristic of the elastic body. However, as the elastic body is pressed to a state where the elastic body is in contact with the restricting wall, the load is rapidly increased with an increase in displacement by a combination of the sliding resistance of the elastic body and the elastic characteristics of the elastic body. As a result, a desirable relationship of the load to the displacement can be obtained.
The contact area of the elastic body with the restricting wall may be enlarged with further progress of pressing of the elastic body. With this configuration, after the pressed elastic body is brought into contact with the restricting wall, the contact area of the elastic body with the restricting wall is enlarged and thereby the sliding resistance of the elastic body is increased. As a result, a desirable smooth relationship of the increased load to the increased displacement can be obtained.
The elastic body may have a hollow portion opened to the restricting wall side, with an intermediate elastic body inserted in the hollow portion. Therefore, when the elastic body is pressed, the intermediate elastic body is compressed, being swelled out of the opening of the hollow portion, and is brought in press-contact with the restricting wall.
When the elastic body is pressed, sliding resistance is generated due to the contact of the elastic body with the restricting wall in addition to the elastic characteristics of the elastic body, and also the sliding resistance of the intermediate elastic body due to the pressing contact of the restricting wall with the intermediate elastic body compressed and swelled from the opening of the hollow portion. As a result, a desirable relationship of the load to the displacement of the elastic body can be easily obtained.
To further achieve the object of the invention, a damping force generating mechanism is provided which includes an elastic body which generates a damping force when being pressed, a hollow portion opened in the elastic body in the direction perpendicular to the pressing direction, an intermediate elastic body inserted in the hollow portion, and a restricting wall provided opposite to the opening of the hollow portion. Thus, when the elastic body is pressed, the intermediate elastic body is compressed, being swelled out of the opening of the hollow portion, and is brought into pressing contact with the restricting wall.
At the beginning of the pressing of the elastic body, elastic characteristics of the elastic body and the intermediate elastic body are generated. However, as the pressing of the elastic body proceeds, the intermediate elastic body is compressed, being swelled out of the hollow portion of the elastic body, and is brought into contact with the restricting wall. Thus, sliding resistance of the intermediate elastic body is generated. As a result, a desirable relationship of the load to the displacement of the elastic body can be easily obtained.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.